WITH SOVIET TROOPS poised on Poland's borders, the United States must act quickly to forestall an invasion. While we cannot directly block the advance of Russia's tanks, we can make it clear that Soviet imperialism will entail a high cost. The courage shown by Polish workers in the last year has earned our admiration and deserves our support in this crisis.

It would be hypocritical of the United States to condemn and oppose Soviet imperialism without ending our support for repressive regimes in El Salvador and South Africa. Our hands, too, are dirty. But to abandon Poland's workers while we redirect our policy towards the Third World would be a grave abdication of responsibility. We must both oppose Soviet aggression and correct our errors.

The memory of Afghanistan, Czechoslovakia and Hungary is vivid. Withdrawing from Olympic competition and introducing resolutions in the United Nations are too feeble responses to Soviet intervention in independent states. We must let the Soviets know that we will not hesitate to prevent the sale of advanced technology, to cut off scientific and cultural exchanges and to bolster our new alliance with China (possibly even with the sale of non-nuclear arms and computer technology) if Soviet troops invade Poland. We should not renounce the SALT negotiation process, engage in a costly arms race or attempt to starve the Soviet people. But we must not wallow in guilt and impotence, either. There is much to be done.